Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley PowerPoint ® Lectures for University Physics, Twelfth Edition – Hugh D. Young and Roger A. Freedman Lectures by James Pazun Chapter 4 Newton’s Laws of Motion

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley What are the properties of force(s)? Combinations of “push” and “pull”

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley There are four common types of forces The normal force— When an object rests or pushes on a surface, the surface pushes back. Frictional forces—In addition to the normal force, surfaces can resist motion along the surface.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley There are four common types of forces II Tension forces—When a force is exerted through a rope or cable, the force is transmitted through that rope or cable as a tension. Weight—Gravity’s pull on an object. This force can act from large distances.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley What are typical sizes for common forces?—Table 4.1

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley How to denote a force—Figure 4.3 Use a vector arrow to indicate magnitude and direction of the force.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Use the net (overall) force—Figure 4.4 Several forces acting on a point have the same effect as their vector sum acting on the same point.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Decomposing a force into components F x and F y are the parallel and perpendicular components of a force to a sloping surface. Use F*Cos θ and F*Sin θ operations to find force components.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Notation and method for the vector sum—Figure 4.7 We refer to the vector sum or resultant as the “sum of forces” R = F 1 + F 2 + F 3 … F n = Σ F. Use Tan θ = R y /R x and R = (R x 2 + R y 2 ) 1/2.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Superposition of forces—Example 4.1 Adding all x components and all y components allows you to add many vectors. Example 4.1 has three.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newton’s First Law—Figure 4.9 Simply stated— “objects at rest tend to stay at rest, objects in motion stay in motion.” More properly, “A body acted on by no net force moves with constant velocity and zero acceleration.”

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newton’s First Law II—Figure 4.10 Figure 4.10 shows an unbalanced force causing an acceleration and balanced forces resulting in no motion. Refer to Conceptual Examples 4.2 and 4.3.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Inertial frames of reference—Figure 4.11 When a car turns and a rider continues to move, the rider perceives a force.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newton’s Second Law—Figure 4.13 An unbalanced force (or sum of forces) will cause a mass to accelerate.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley An object undergoing uniform circular motion Refer to Figure We have already seen the centripetal acceleration. But, if we measure the mass in motion, Newton’s Second Law allows us to calculate the centripetal force.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The relationship of F, m, and a Because a depends linearly on m and F, an acceleration will be directly proportional to the applied force. Solution of the units gives a new combination of (kg*m)/s 2 for the force. This is called… the Newton.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The relationship of F, m, and a redux Because a depends linearly on m and F, an acceleration will be inversely proportional to the object’s mass.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Using the Second Law—Example 4.4 Refer to Example 4.4, using Figure 4.18.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Using the Second Law II—Example 4.5 Refer to Example 4.5, using Figure 4.19.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newtons, kilograms, pounds, and slugs—Table 4.2 Table 4.2 rightly points out that the pound is a force. The popular culture refers to it as a weight (which is actually a slug). The Dyne is actually a cgs version of the Newton (sometimes used with fine work on tiny objects).

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Many have asked “how lethal is a coin dropped from atop a tall building”? Urban legends have said that a penny dropped from the top of the Empire State Building can kill. Conceptual Question 4.6 ponders this enigma with a euro. Cable TV has allowed those two science guys who test such “myths” to debunk this one.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley g, and hence weight, is only constant on earth, at sea level On Earth, g depends on your altitude. On other planets, gravity will likely have an entirely new value. Example 4.7 examines “apparent weight” in a rapidly stopping car.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newton’s Third Law Exerting a force on a body results in a force back upon you. Figure 4.25 shows “an action–reaction pair.” See Example 4.8.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newton’s Third Law—Objects at rest An apple on a table or a person in a chair—there will be the weight (mass pulled downward by gravity) and the normal force (the table or chair’s response).

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Newton’s Third Law—Objects in motion An apple falling or a refrigerator that needs to be moved—the first law allows a net force and mass to lead us to the object’s acceleration.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Free-body diagrams—Figure 4.30 A sketch then an accounting of forces